Modular humeral prosthesis and method

ABSTRACT

A modular humeral prosthesis for replacement of the humeral head of a humerus. The prosthesis generally comprises a stem to be fitted to a resected humerus; a head sized and configured to approximate the humeral head; and an intermediate connecting member for connecting the stem to the head. The intermediate connecting member provides a desired angle of inclination or offset between stem and head. The head may be a traditional humeral head, or it may be an eccentric humeral head, with its mating portion being offset. The head may also comprise a groove or milled trench at least partially surrounding or otherwise defining mating portion. Also disclosed is a modular humeral prosthesis kit comprising a variety of different intermediate connecting members that may be selected to tit the prosthesis to the patient, and a method of replacing a humeral head in a patient.

[0001] This application is a continuation in part of U.S. Serial No.09/054,709 entitled “MODULAR HUMERAL PROSTHESIS AND METHOD” by Dews, theentire contents of which is hereby incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] During the procedure of a shoulder replacement operation, atleast a portion of the proximal section of the humeral shaft will bereplaced by a metal prosthesis. This prosthesis will generally consistof two parts: a stem that is mounted into the medullary canal of thehumerus, and a head component connected in some manner to the stem. Thehead component replaces the bearing surfaces of the humerus andarticulates with the surface of the scapula to allow the movement of theshoulder.

[0003] Modular humeral prostheses are known. The stem and head componentmay be supplied in “modular” form, that is, as separate connectablecomponents. Different stem sizes and head sizes in a modular implantdesign provide the surgeon with some degree of inter-operativeflexibility, which facilitates reconstruction of the original anatomy ofthe patient.

[0004] With a range of stem sizes and a range of head sizes available,the surgeon can choose a particular combination to suit the anatomy ofeach individual patient without having to stock a large inventory of“integral” or “unitary” humeral prostheses. As used herein, “integral”and “unitary” mean formed in one continuous piece in contrast to theseparate connectable components of a modular prosthesis. For example,one patient might require a relatively small head and a relatively longstem. With a unitary prosthesis a wide range of stem lengths would berequired for each head size whereas with a modular arrangement aparticular head can be used with a range of stem sizes and visa versa.

[0005] Additional variations arise also as a result of individualpatients requiring differing angles of inclination of the head relativeto the stem and differing offsets between the axis of the head and theaxis of the stem. Thus, in one patient the offset may be posterior andin another anterior.

[0006] Various shoulder prostheses are disclosed in European PatentPublication No. EP-A 0 679 375 to Odella dated Sep. 2, 1998; EP-A 0 712617 to Walch, et al. dated Sep. 29, 1999; French Patent No. FR-A 2 664809 to Travers dated Dec. 26, 1997; U.S. Pat. Nos. 3,694,820 to Scales,et al. dated Oct. 3, 1972; 3,803,641 to Golyakhousky dated Apr. 16,1974; 4,045,825 to Stroot dated Sep. 6, 1977; 4,106,130 to Scales datedAug. 15, 1978; 4,179,758 to Gristina dated Dec. 25, 1979; 4,865,605 toDines, et al. dated Sep. 12, 1989; 4,919,670 to Dale, et al. dated Apr.24, 1990; 5,358,526 to Tornier dated Oct. 25, 1994; 5,549,682 to Roydated Aug. 27, 1996; 5,462,563 to Shearer, et al. dated Oct. 31, 1995and 5,702,457 to Walch, et al. dated Dec. 30, 1997; and PCTInternational Patent Publication No. WO 96/17553 to McDaniel, et al.dated Jun. 13, 1996, which are all incorporated herein by thisreference.

SUMMARY OF THE INVENTION

[0007] This invention provides a modular prosthesis in which a humeralhead, chosen to suit a patient, is attached to a stem chosen to suit theresected humerus of the patient by means of an intermediate connectingmember. The prosthesis can accommodate a wide range of variation in, forinstance offset and/or angle, in a relatively inexpensive and efficientmanner, by accommodating the variations in the intermediate connectingmember rather than in the head.

[0008] Additionally, prostheses according to the present invention caninclude a traditional modular humeral head as well as an eccentricmodular humeral head. The eccentric head features a portion that isoffset from the radial center of the humeral head that cooperates withthe intermediate connecting member. This eccentric head embodiment worksin conjunction with the intermediate connecting member, allowing thesurgeon even further variations and options during the surgery.

[0009] The modular humeral prosthesis generally comprises a stem adaptedto be fitted to a resected humerus, a head adapted to approximate thesize and shape of a humeral head, and an intermediate connecting memberfor connecting the stem to the head. The intermediate connecting memberincludes two connecting surfaces or other engagement structure. Thefirst connecting surface is adapted to cooperate with a structureforming part of the stem in order to mount the intermediate connectingmember to the stem. The second connecting surface is adapted tocooperate with a structure forming part of the head in order to mountthe head to the intermediate connecting member. Preferably, the secondconnecting surface is partially nested with the first connectingsurface. The connecting surfaces are preferably surfaces of rotationhaving axes of rotation, so that they are provided with a full range ofrotational motion.

[0010] For example, the first connecting surface or engagement means formounting the intermediate connecting member on the stem, may have anaxis about which the intermediate connecting member can be rotatedthrough 360° relative to the stem and thereafter secured at a selectedrelative orientation. The second connecting surface or engagement meansfor mounting the head on the intermediate connecting member may have anaxis about which the head can be rotated through 360° relative to theintermediate connecting member and thereafter secured at a selectedrelative rotation.

[0011] In one embodiment, the axes of rotation of the first and secondconnecting surfaces are not coincident or collinear, allowing the headto be given a desired offset relative to the stem.

[0012] In another embodiment, the axis of rotation of the first andsecond connecting surfaces are not parallel, allowing a desiredinclination of the head relative to the stem. Furthermore, the first andsecond connecting surfaces of the intermediate connecting member may bepositioned relative to one another to provide a desired separationbetween the head and the stem. Preferably, the separation or “necklength” between the head and the stem is no greater than 5 mm, but thismay vary depending upon surgeon preferences.

[0013] In a further embodiment, the connecting surfaces provide both anoffset and an angle of inclination, so that in use, the head is offsetand angled relative to the stem.

[0014] Also, the first and second connecting surfaces may each comprisea male or female portion, and the head and stem are provided withcorresponding mating portions. The male and/or female portionspreferably each have a substantially circular cross-sections, and asubstantially self-locking tapered configuration (i.e., a Morse taper).A “Morse taper” is taper that forms an angle providing a self-lockingfunction.

[0015] It is possible for a bore to be provided through the first andsecond connecting surfaces that extends through the intermediateconnecting member, the prosthesis further comprising a fastener insertedthrough the bore to engage the stem further to secure the intermediateconnecting member to the stem.

[0016] In another aspect of the invention, a modular humeral prosthesiskit is provided for replacement of the humeral head of a humerus. Thekit generally comprises a stem adapted to be fitted to a resectedhumerus, a head sized and configured to approximate the humeral head,and a plurality of intermediate connecting members of which one may beselected to connect the stem to the head. Each intermediate connectingmember includes a first connecting surface for mounting the intermediateconnecting member on the stem, and a second connecting surface formounting the head on the intermediate connecting member. The pluralityof the intermediate connecting members of the kit include:

[0017] A. at least one intermediate connecting member in which the firstand second connecting surfaces share an axis of rotation;

[0018] B. at least one intermediate connecting member in which the firstand second connecting surfaces are offset from each other; and

[0019] C. at least one intermediate connecting member in which the firstand second connecting surfaces are inclined at an angle relative to eachother.

[0020] In another embodiment, the plurality of intermediate connectingmembers of the kit include:

[0021] A. at least one intermediate connecting member in which the firstand second connecting surfaces have generally parallel and coincidentcentral axes;

[0022] B. at least one intermediate connecting member in which the firstand second connecting surfaces have generally parallel but notcoincident central axes;

[0023] C. at least one intermediate connecting member in which the firstand second connecting surfaces have an angle of inclination between oneanother that is different than the angle of inclination between thefirst and second connecting surfaces of another intermediate connectingmember of the kit; and

[0024] D. at least one intermediate connecting member in which the firstand second connecting surfaces are separated by a different neck lengththan the neck length separating the first and second connecting surfacesof another intermediate connecting member of the kit.

[0025] The specifications for the plurality of intermediate connectingmembers described above may be met by combining features in some of theintermediate connecting member of the kit. For example, two intermediateconnecting members may have different neck lengths, angles ofinclination and offsets or zero offset.

[0026] Preferably, the first connecting surface of each intermediateconnecting member has an axis about which the intermediate connectingmember can be rotated through 360° relative to the stem and thereaftersecured at a selected relative orientation, and the second connectingsurface of each intermediate connecting member has an axis about whichthe head can be rotated through 360° relative to the intermediateconnecting member and thereafter secured at a selected relativerotation.

[0027] Preferably, the first connecting surface of each intermediateconnecting member comprises a female portion, and the stem is providedwith a corresponding mating male portion, and the second connectingsurface comprises a male portion having the first connecting surfacenested therein, and the head is provided with a corresponding matingportion, such as a female cavity. Most preferably, the male and femaleportions each have a substantially circular cross-section, and asubstantially self-locking tapered configuration (i.e., a Morse taper).

[0028] In a further embodiment, the surgeon is provided with the optionof using a traditional humeral head, having its corresponding matingportion at the approximate center of the radius of the humeral head, orusing an eccentric humeral head, having its corresponding mating portionoffset from the center of the radius of the humeral head.

[0029] According to other aspects of the invention, methods of replacinga humeral head in a patient generally comprise:

[0030] (a) Resecting the proximal end of the humerus to remove the headand expose the medullary canal of the humerus;

[0031] (b) Inserting the stem of a prosthesis into the medullary canalof the resected humerus, the prosthesis being modular and comprising:

[0032] (i) a stem;

[0033] (ii) an eccentric humeral head; and

[0034] (iii) one of a plurality of intermediate connecting members forconnecting the stem to the head; each intermediate connecting memberincluding:

[0035] a first, female, connecting surface forming a cavity that isadapted to receive a structure that protrudes from the stem in order tomount the intermediate connecting member to the stem; and

[0036] a second, male, connecting surface adapted to be received in acavity in the head in order to mount the head to the intermediateconnecting member,

[0037] the second connecting surface at least partially nested with thefirst connecting surface;

[0038] the plurality of intermediate connecting members including atleast some members having different angles of inclination between theirfirst and second connectors;

[0039] (c) selecting a particular intermediate connecting member toprovide a desired angle of inclination of the head relative to thehumerus; and

[0040] (d) mounting and locking the intermediate connecting member tothe stem, and mounting and locking the intermediate connecting member tothe head, the mounting and locking of the intermediate connecting memberto the stem and head imparting any desired angle of inclination of thehead relative to the humerus.

[0041] The plurality of intermediate connecting members may includeintermediate connecting members having different neck lengths separatingthe first and second connecting surfaces, and the methods furthercomprise selecting an intermediate connecting member to provide adesired separation between the head and the stem.

[0042] The surgeon will still need her traditional range of head sizesand stem sizes and lengths. However, the surgeon does not needadditional heads or stems to provide a particular orientation of thehead or a particular offset for the head, although the surgeon mayprefer to use the eccentric head option described herein. Thus, while arange of intermediate connecting members are required to be available tochoose particular offsets and orientations, those intermediateconnecting members are relatively inexpensive compared with the normallyconsiderable cost of the highly sophisticated head component.

[0043] Also, it is an advantage of the invention that the surgeon canchoose quite independently of one another the three component parts.Thus, the surgeon does not have to be concerned with questions of offsetand orientation when selecting the right head size, except to the extentthat she prefers to use an eccentric head. The same is true as regardsthe stem: the surgeon can choose the correct stem to fit the medullarycanal in the humerus and so give a long lasting and secure joint betweenthe stem and the bone. Having selected these components, the surgeoncan, quite independently, decide on the particular offset and/ororientation of the head relative to the stem and select an intermediateconnecting member accordingly. The surgeon is, therefore, able to matchthe modular prosthesis used to the original anatomy of a particularpatient. Because a shoulder joint is enclosed and surrounded by softtissue, it is preferable (but not necessary) that the spacing betweenthe end of the stem and the head be kept to a minimum, e.g. no greaterthan 5 mm.

[0044] The typical surgical procedure for the implantation of a humeralprosthesis includes the determination of the longitudinal axis of thehumerus, drilling a hole in the proximal margin between the head and thetuberosity in line with this, then inserting a starter reamer or broach,and developing a bore hole along the longitudinal axis of the humerus.Next, this bore hole can be enlarged by using progressively largerreamers or broaches, until the surgeon determines that the reamer orbroach being used is the largest possible fit into the available cavitywithout the excessive removal of cortical bone. Then, the head isaccurately removed from the proximal portion of the humerus, and a flatangled face is prepared on the proximal portion of the humerus, usuallyalong the line of the anatomical neck, by means of a resection guide.

[0045] The cavity thus prepared, the trial stem can be introduced. Atthis stage, the surgeon is able to determine the amount of anteversionthat is appropriate for the patient. Once in place, the head measurementinstrument can be attached, and the trial head attached to this. Thishead measurement instrument allows the accurate placement of the head ina number of different positions so that the surgeon can assess whichposition best suits the anatomy of the patient. Once determined, thesurgeon can, in one aspect of the invention, read off the specificorientation of the head from a scales or indicia on the instrument; thisdetermines which intermediate connecting member is to be used with thedefinitive implant.

[0046] It is not possible to provide an infinite number of intermediateconnecting members so as to cover every possibility of adjustment. Inpractical terms, therefore, one provides a range of intermediateconnecting members in incremental sizes to provide a range of discreteadjustments in just the same way that a discrete number of heads andstems are provided. However, because the connecting surfaces allow therelative rotation of the components, one can with a single intermediateconnecting member choose an amount of offset and that amount can bepositioned on a locus throughout 360°. The same, of course, is true asregards the inclination of the axis of the head relative to the stem.

[0047] Another reason that having a range of intermediate connectingmembers is helpful to the surgeon is because it allows the surgeon toreplace the intermediate connecting member without removing the entirestem. For example, in a revision surgery, the surgeon may want to changethe angulation or the offset of the head member with respect to the stemwithout removing the stem. Providing the surgeon with an intermediateconnecting member allows the surgeon to use the intermediate connectingmember to angulate the head with respect to the stem or offset the headwith respect to the stem without requiring a whole new implant. Thesurgeon can use the intermediate connecting member to change inclinationor offset so that the head will correspond appropriately to the stem.

[0048] In a preferred embodiment of the invention, the intermediateconnecting member is available in a discrete number of sizes, each sizeproviding an incremental increase in the separation between the twoconnecting surfaces. Thus, the surgeon is provided with a variety ofparts from which to choose in order to approximate best the patient'soriginal anatomy by selecting a part that will provide the closestapproximation of the original separation between the humeral head andthe humeral stem.

[0049] It is preferred that the second connecting surface be located atthe center of the base of the humeral head. Thus, in this embodiment,the relative rotational placement of the head component has no effect inaltering the angle of inclination of the head or the axial offset of thehead in relation to the stem or even the separation between the head andthe stem. If the surgeon desires that the humeral head itself shouldhave an offset, she may use an eccentric head in conjunction with theintermediate connecting member. It is not essential that the secondconnecting surfaces be of circular cross-section although this ispreferred. This provides the advantage that fewer of the expensive headcomponents are required to achieve this range of variables. Naturallythe head will have to be provided in a number of incrementally varyingsizes to fit the needs of each individual patient's scapula or glenoidprosthesis. Additionally, in an alternate embodiment, there are alsoprovided eccentric heads in a number of incrementally varying sizes. Theportion of the connecting surface forming part of the intermediateconnecting member can both be male or alternatively one can be male andthe other female.

[0050] It is further preferable that the connecting surfaces will eachbe of a substantially cylindrical shape, whether male or female, andtherefore allow the intermediate connecting member to be rotatablerelative to the stem and the head rotatable relative to the intermediateconnecting member before securement. To fix one part relative to theother the cylinders of the male and female portions are preferably ofthe Morse taper type. This fixing may be supplemented by a screw orother fastener fixation. In order to satisfy the criterion for strength,it is desirable that the intermediate connecting, member be formed inone piece. It is, however, within the scope of this invention that theintermediate connecting member be formed from a plurality of pieces.

BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Embodiments of the invention will now be described by way ofexample and with reference to the accompanying schematic drawings, inwhich:

[0052]FIG. 1 is an exploded side elevation of a modular humeralprosthesis according to the invention;

[0053]FIG. 2 is the assembled prosthesis of FIG. 1;

[0054] FIGS. 3-7 are various intermediate connecting members accordingto the invention;

[0055]FIG. 8 is an exploded side elevation of a second embodiment of themodular humeral prosthesis according to the invention; and

[0056] FIGS. 9-13 are various intermediate connecting members accordingto another embodiment of the invention.

[0057] FIGS. 14-16 are various intermediate connecting members accordingto a further embodiment of the invention.

[0058]FIG. 17 is a bottom plan view of a preferred embodiment of aneccentric head according to the invention.

[0059]FIG. 18 is a bottom plan view of the eccentric head of FIG. 17,having a milled trench.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

[0060] The stem 10 shown in FIG. 1 is available in a number of differentsizes to match the size to which the medullary canal 12 has been reamedor broached. The shaft of the stem 14 is designed to contact thepreviously reamed or broached medullary canal 12 and extend into theremaining humerus to prevent any undesired movement of the stem 10.

[0061] The stem 10 may be prevented from rotating by the use of fins 16located at the neck of the stem 10. These fins 16 are wedged into theproximal position of the humerus to prevent any undesired movement ofthe stem 10 and offer some additional support to the face 18 of the stem10. The face 18 of the stem 10 fits onto the previously prepared face ofthe humerus 20, and is designed so that the angle of the face 18 isroughly equal to that of the anatomic neck of the humerus. CoassignedU.S. patent application Ser. No. 08/946,758, filed Oct. 8, 1997, and PCTInternational patent application No. US97/18207, filed Oct. 8, 1997,both by Michel Mansat et al disclose a shoulder prosthesis with fins,and are incorporated herein by reference.

[0062] The humeral head 22 is designed to articulate with the scapula orglenoid prosthesis (not shown). The head 22 replaces the articulatingsurface of the humerus and is largely hemispherical in shape. A varietyof sizes of head 22 are provided to complement the patient's scapula orglenoid prosthesis. The articulating surface of the head 22 is highlypolished to reduce friction, hence wear, on the scapula or glenoidprosthesis.

[0063] Based on proximal humeral morphology, the humeral head center ofthe preferred embodiment is generally medialized and offset posteriorlyfrom the humeral canal. In fact, there is about a 3 mm posterior offsetin an average individual. In order to provide optimal proximal humeralbone coverage, it is useful to provide the surgeon with the option ofusing an eccentric head 200, shown in FIG. 17.

[0064] As with a traditional humeral head, eccentric humeral head 200 isalso designed to articulate with the scapula or glenoid process.However, instead of having a centered mating portion, head 200 accordingto the preferred embodiment has an eccentric mating portion 202.Eccentric mating portion 202 is not coaxial with the head, i.e., it isoffset from the center of the humeral head articular radius. Thiseccentricity helps to align the proximal humeral stem with the glenoid,providing a shift in the normal anatomy.

[0065] Eccentric humeral head 200 is shown as having a female taper thatis offset from the center of the humeral head articular radius. Itshould be understood, however, that mating portion 202 may be anyconnecting structure, such as a male mating portion, a tapered matingportion (whether or not male), and the like. The essence of theinvention is that the humeral head itself displays eccentricity. Thiseccentricity may range from 1 mm to 5 mm. If eccentric head 200 is usedin conjunction with an intermediate connecting member, it allows thesurgeon to achieve more options to fit various patient geometries.

[0066] The variation in patient anatomy, inclination angle,retroversion, and posterior offset of the humeral head necessitate theneed for a multitude of intra-operative adjustments. Eccentric head 200allows the surgeon during surgery to adjust for inclination,retroversion, and/or eccentricity. During intra-operative trialing,which the surgeon performs in order to place the correct amount oftension on the soft tissue and supporting tendons, the proper humeralhead size (height and diameter) is initially selected. The eccentrichumeral head 200 enables the surgeon to adjust the humeral headprosthesis in order properly to position the humeral head in an optimumposition with respect to the glenoid articular surface, as well as withrespect to the tuberosity attachment site. The ability to adjust theeccentricity in the plane of the selected inclination angle along withthe ability to adjust retroversion is a distinct advantage in achievingoptimal joint balancing and increased range of motion.

[0067] For example, if the surgeon wishes to vary the inclination angleor provide an offset of the head with respect to the stem, use of anintermediate connecting member, described below, can help achieve thisconfiguration. However, if the surgeon wishes to alter the retroversionangle of the center of the head with respect to the glenoid, the use ofeccentric head 200 helps achieve this configuration. An eccentric headused in conjunction with an intermediate stem member allows the surgeonto vary inclination, retroversion, eccentricity and offset, providingthe surgeon with an increased range of usability and possibilities tofit various patient features or irregularities.

[0068] Of course, eccentric head 200 may be employed with or without anintermediate connecting member. In other words, the eccentric headdescribed herein may be used coupled directly to the humeral stem. Itmay also be used in conjunction with an intermediate connecting memberthat has an offset, that provides an angle, or a combination of both orneither. Additionally, eccentric head 200 may be used as an actualimplant or as part of a trialing system or method. An exemplary trialingmethod is described in copending Provisional Application U.S. Ser. No.60/201,503 to Hartdegen filed May 3, 2000, Attorney Docket Number10557/200809, incorporated herein by reference.

[0069] In a further embodiment, as shown in FIG. 18, eccentric head 200has a female mating portion and trench 204 or groove defining matingportion 202. Trench 204 is any groove, indentation, or removed portionthat may be milled, molded or otherwise formed. It is locatedcircumferentially around and substantially surrounds or otherwisedefines mating portion 202. Trench 204 may extend the entirecircumference of the inside of the humeral head, or it may be divided bydistraction slots 206 as shown in FIGS. 17 and 18.

[0070] Trench 204 preferably extends to the edge of the modular humeralhead. Trench 204 may be any depth, but preferably extends to the bottomof the taper, approximately ten millimeters, though it is possible toprovide a shallower trench 204. It is preferred that trench 204 extendto the depth at which the head and stem engage when in use. Put anotherway, trench 204 should extend to the depth where modular humeral headfully cooperates with the end of intermediate connecting member or stemwhen in use.

[0071] Providing a trench 204 on eccentric head 200 imparts a number ofadvantages. It provides increased distraction forces, so that when thesurgeon impacts the head on the stem, the head provides superior lockingforces with respect to the stem taper or intermediate connectingportion. It should be noted that trench 204 may achieve the describedadvantages if provided on either eccentric head 200 or on a traditionalhumeral head. It should also be noted that any head having a trench 204may be used with or without an intermediate connecting member. Forpurposes of this document, reference to head 22 also includes areference to eccentric head 200, a head with a trench 204 (whethertraditional or eccentric), or both.

[0072] In use, it is believed that trench 204 allows the female taper toexpand, creating hoop stress, which are tensile stresses alongcircumference of taper/lock interface. The increased tensile stresseshelp hold the two tapers together and thereby increase distractionforces between the two mating surfaces.

[0073] Without limitation to any theory, it is believed that the trench204 allows taper to receive and seat further the portion with which itconnects (whether it be the connecting surface of intermediateconnecting member or the stem). As the taper expands, the portion withwhich it connects can seat even further and deeper into the taper,providing increased locking forces. To the contrary, a solid head nothaving trench 204 does not provide this benefit because there is no roomfor the taper to expand. Trench 204 on head 200 strengthens theattachment of the head to a corresponding component.

[0074] Currently, other device manufacturers offer only eccentric heads.However, consideration must be given to the locking device when thecenter line of the Morse tapers are not co-axial. The ability of theeccentric head to provide a substantial lock with respect to the stemtaper or intermediate member has not been considered in current designs.This invention provides, in preferred embodiments, a superior lockingmeans by the presence of a trench 204, which provides an increase intaper locking strength. The addition of the trench 204 provides theopportunity to provide up to at least 5 mm of eccentricity, an optionthat no other system currently provides.

[0075] Because of the increased distraction forces that are required toremove the head from the stem, eccentric head 200 is shown havingdistraction slots 206. Distraction slots 206 provide an opening, whichallows the surgeon to use an osteotome or other instrument to apply alever-type motion to more easily remove the head from the stem.

[0076] An intermediate connecting member 24 as shown in FIG. 1 has firstand second male tapers 26 and 28 of the “Morse taper” type. Once pushedtogether two Morse taper parts tend to stay together. The first taper 26is designed to connect with the stem 10 and the second taper 28 with thehead 22. The tapers 26 and 28 are aligned in generally oppositedirections for mating with a female taper 30 of the stem 10 and a femaletaper 32 of the head 22.

[0077] The first male taper 26 may also be held onto the female taper 30of the stem 10 by means of a locking screw 34, which fits into acounter-bored hole 36 in the intermediate connecting member 24. The axisof this counter-bored hole 36 is aligned along the central axis of thetaper 26 and the screw fits into this counter-bored hole 36 and locatesinto a threaded hole 38 in the stem 10.

[0078] The male tapers 26, 28 of the intermediate connecting member 24can be securely connected with the respective female tapers 30, 32 ofthe stem 10 and head 22, which are also of the Morse taper type andmatch the tapers of the intermediate connecting member 24 by applying anexternal force, to form an interference fit between the mating tapers 24and 30, and 26 and 32, as shown in FIG. 2.

[0079] The first and second male tapers 26 and 28 constitute oneembodiment of the first and second connecting surfaces of theintermediate connecting member 24. Alternatives include other connectingor mating parts that define the relative orientation and position of thehead 22 and the intermediate connecting member 24 or the stem 10 and theintermediate connecting member 24. For example, the first and/or secondmale tapers 26 and 28 could be replaced by female tapers (not shown) andthe female tapers 30 and 32 of the stem 10 and/or head 22 replaced bymale tapers (not shown).

[0080] There can be a large variety in the shape, size and orientationof human humeral bones and therefore it is desirable to tailor thehumeral prosthesis to suit each individual case. The various designs ofintermediate connecting members of the present invention provide aconsiderable range of different head positions and orientations relativeto the humeral stem that can be selected and connectedinter-operatively.

[0081] The position of the head 22 can be varied by using differentintermediate connecting members 24 as are appropriate in each individualcase. Various designs of intermediate connecting members 24 a-a areillustrated in FIGS. 3 to 7.

[0082] In each of these cases the intermediate connecting member 24 a-ehas the same elements and is joined to the stem 10 and head 22 asdescribed above.

[0083] One configuration of an intermediate connecting member 24 a isillustrated in FIG. 3. In this configuration, the first male taper 40and the second male taper 42 are axially aligned with minimum separationor “neck length” 44 between them. The design of this intermediateconnecting member 24 a matches the anatomical design of some patients'original humerus.

[0084] For other patients, a larger separation between the head 22 ofthe humeral prosthesis and a fixed point on the stem 10 is moreappropriate. To meet this requirement, the intermediate connectingmember 24 b of FIG. 4 is used. In this design, a portion of theintermediate connecting member 24 b between the two tapers 50 and 52 isavailable in a number of incrementally different sizes to allow thesurgeon to select the appropriate separation or “neck length” 54 betweenthe tapers 50 and 52, and hence the separation between the head 22 andstem 10 of the prosthesis.

[0085] The anterior or posterior offset can be simulated using thedesign of intermediate connecting member 24 c as shown in FIG. 5 tomimic offsets 66 that can naturally occur in the humerus. In thisdesign, the central axes of the first and second male tapers 60 and 62are parallel and offset from one another as illustrated at 66. Thesecond male taper 62 is counter-bored at an off-center position (e.g.,compare bore 68 or FIG. 5 with bores 48 and 58 of FIGS. 3 and 4). Thisallows the head 22 to be attached on a parallel but not coincident axisto the first male taper 60, and thus to the female taper 30 of the stem10. Again, this design is available in a number of incrementallydifferent offsets 66 so the surgeon can select the most appropriateintermediate connecting member 24 c for each individual patientinter-operatively.

[0086] The angle of inclination α of the humeral head relative to theaxis of the humeral stem can vary from patient to patient. Theintermediate connecting member 24 d can simulate this orientation. Thedesign shown in FIG. 6 comprises a portion of the intermediateconnecting member 24 d that has a generally wedge shaped design. Thesurgeon will be able to select the wedge-shaped intermediate connectingmember 24 d from a range of intermediate connecting members 24 d havingincremental difference in the inclination angle a as shown in FIG. 6, tobest fit each individual patient. Due to the wedge-shape, the centralaxes of the first and second male tapers 70 and 72 of this design areoffset from parallel by an angle equal to the inclination angle α.

[0087] Any of the features of intermediate connecting members 24 a-dillustrated in FIGS. 1 to 6 can be combined to provide the desiredvariation in neck length 44, 54, 84 anterior or posterior offset 66, 86or angular inclination a to best suit each individual patient's anatomy.

[0088]FIG. 7 shows an intermediate connecting member 24 e that includesa combination of the angular inclination α as described in FIG. 6, theanterior/posterior offset 86 as depicted in FIG. 5, and the taperseparation 84 as illustrated in FIG. 4.

[0089] In the above embodiments, the male members of the two connectingsurfaces are provided by the intermediate connecting member 24 a-e. Inan alternative embodiment one or both of the two connecting surfacesprovided by the intermediate connecting member may comprise femaleportions. For example, FIG. 8 illustrates a second embodiment of themodular humeral prosthesis 100 of the invention similar in many respectsto the first embodiment shown in FIGS. 17. Differences include theprovision of a male tapered connecting portion 102 on the stem 104, anda female tapered connecting portion 106 on the intermediate connectingmember 108.

[0090] Male connecting portion 102 and female connecting portion 106 aredesigned for substantially self-locking mating, and preferably have acircular cross section The self-locking function may be accomplished byproviding a “Morse taper” on the male and female connecting portions 102and 106. The female connecting portion 106 constitutes a secondembodiment of the first connecting surface of the intermediateconnecting member 108.

[0091] Optionally, a fastener 110 may be inserted through a bore 112through the intermediate connecting member 108 and into engagement witha bore 114 in the stem 104 to further secure the female connectingportion 106 of the intermediate connecting member 108 on the stem 104. TFastener 110 and the bore 114 are provided with interlocking threads. Asan alternative embodiment, the male and female connecting portion 102and 106 could be provided with a non-self-locking configuration; inwhich case the fastener 110 or another locking mechanism would take on agreater importance.

[0092] As is the case with the first embodiment, the head 114 of thesecond embodiment is provided with a female connecting portion 116, andthe second connecting surfaces of the intermediate connecting member 108comprises a male connecting portion 118. The female and male connectingportions 116 and 118 are also preferably provided with a self-lockingtapered configuration, i.e., a Morse taper.

[0093] FIGS. 9-13 illustrate various intermediate connecting members 108a-a for use in the prosthesis 100. FIGS. 9 and 10 illustrate twointermediate connecting members 108 a and 108 b providing two differentseparations 120 and 122. In this respect, intermediate connecting member108 a is similar to intermediate connecting member 24 a of the firstembodiment (FIG. 3) due to the minimal separation 120 or 44, andintermediate connecting member 108 b is similar to intermediateconnecting member 24 b of the first embodiment (FIG. 4) due to thegreater separation 122 or 54. Both intermediate connecting member 108 aand 108 b show a zero inclination angle and a zero offset.

[0094]FIG. 11 illustrates another intermediate connecting member 108 chaving, like member 108 a, minimal separation. Intermediate connectingmember 108 c, however, has a non-zero offset 124. This non-zero offset124 is accomplished by displacing or offsetting the central axis or axisof rotation of the female locking portion 126 relative to the centralaxis of axis of rotation of the male locking portion 128 by the offset124. In this respect, the intermediate connecting member 108 c issimilar to the intermediate connecting member 24 c of the firstembodiment (FIG. 5).

[0095]FIG. 12 illustrates yet another intermediate connecting member 108d having, like member 108 a, minimal separation and zero offset.Intermediate connecting member 108 d, however, has a non-zeroinclination angle β. Inclination angle β is similar in function andpreferred magnitude to the inclination angle α discussed with respect tothe first embodiment (e.g., FIG. 6).

[0096]FIG. 13 illustrates an intermediate connecting member 108 e havinga non-zero separation 130, a non-zero offset 132 and a non-zeroinclination angle β. In this respect, intermediate connecting member 108e is similar to intermediate connecting member 24 e of the firstembodiment (FIG. 7).

[0097] FIGS. 14-16 are various intermediate connecting memberscorresponding to FIGS. 11-13, but showing the tapered locking portionsin more detail.

[0098] One consequence of the design of the second embodiment of theprosthesis is that the male connecting portion 118 may have a lengthextending into the intermediate connecting member, e.g., 108 a, adistance sufficient that it is received both in the intermediateconnecting member 108 a and the void defined by the female connectingportion 116 of the head 114. This is accomplished without any directengagement between the male connecting portion 118 of the stem 104 andthe female connecting portion 116 of the head 114.

[0099] Other embodiments, which are not illustrated in the drawing,include (1) the first connecting surfaces comprising a male connectingportion and the second connecting surfaces to comprising a femaleconnecting portion, and (2) both the first and second connectingsurfaces comprising female portions.

[0100] In summary, at least one advantage of providing an eccentrichumeral head along with an intermediate connecting member having anangulation and/or inclination is that although the intermediateconnecting member can change the medial offset (offset from glenoid tohumeral canal), the eccentric head helps align the humeral head with theglenoid (to account for natural offset in anatomy.) In other words, eventhough the intermediate connecting member can change the retroversionangle, the humeral head may still not be in center of glenoid. Theeccentric head helps provide this alignment. Put another way, theintermediate connecting member provides the ability to adjust theinclination angle and retroversion angle. The addition of eccentric head200 provides the surgeon with ability to adjust for the posterior offset(i.e., eccentricity) of the humeral head in the plane of the adjustedhumeral head.

[0101] As various changes could be made in the above constructions andmethods without departing from the scope of the invention as defined inthe claims, it is intended that all matter contained in the abovedescription or shown in the accompanying drawings be interpreted asillustrative and not in a limiting sense.

What is claimed is:
 1. A modular humeral prosthesis for replacement ofthe humeral head of a humerus, comprising: (a) a stem adapted to befitted to a resected humerus; (b) an eccentric head adapted toapproximate the size and shape of a humeral head, having an eccentricmating portion adapted to interface with an intermediate connectingmember; (c) an intermediate connecting member for connecting the stem tothe head, the intermediate connecting member including: a firstconnecting surface that is adapted to cooperate with structure formingpart of the stem in order to mount the intermediate connecting member tothe stem; and a second connecting surface adapted to cooperate withstructure forming part of the head in order to mount the head to theintermediate connecting member, the second connecting surface at leastpartially nested with the first connecting surface and the first andsecond surfaces being surfaces of rotation having axes of rotation, theaxis of rotation of the first surface non-collinear with the axis ofrotation of the second surface.
 2. A prosthesis according to claim 1 inwhich both connecting surfaces are adapted to lock to correspondingstructure using a tapered locking mechanism.
 3. A prosthesis accordingto claim 1 in which the second connecting surface is inclined at anangle relative to the first connecting surface.
 4. A prosthesisaccording to claim 1 in which each of the first connecting surface andthe second connecting surface has an axis, and in which said axes areoffset from each other in order to cause the first connecting surface tobe offset from the second connecting surface.
 5. A prosthesis accordingto claim 1 in which (a) the second connecting surface is inclined at anangle relative to the first connecting surface; and (b) the secondconnecting surface is offset from the first connecting surface.
 6. Amodular humeral prosthesis according to claim 1 in which the firstconnecting surface is a female connecting surface and the secondconnecting surface is a male connecting surface.
 7. A modular humeralprosthesis according to claim 1 in which the eccentric head comprises atrench at least partially surrounding the eccentric mating portion.
 8. Amodular humeral prosthesis for replacement of the humeral head of ahumerus, comprising: (a) a stem adapted to be fitted to a resectedhumerus; (b) an eccentric head adapted to approximate the size and shapeof a humeral head, having an eccentric mating portion adapted tointerface with an intermediate connecting member; (c) an intermediateconnecting member for connecting the stem to the head, the intermediateconnecting member including: a first connecting surface forming atapered, generally frustoconically shaped, cavity that is adapted tocooperate with a structure forming part of the stem in order to mountand lock the intermediate connecting member to the stem; and a secondconnecting surface that is generally frustoconically shaped, tapered,and adapted to cooperate with structure forming part of the head inorder to mount and lock the head to the intermediate connecting member,the second connecting surface at least partially nested with the firstconnecting surface and the first and second surfaces being surfaces ofrotation having axes of rotation, the axis of rotation of the firstsurface non-collinear with the axis of rotation of the second surface.9. A prosthesis according to claim 8 in which the second connectingsurface is inclined at an angle relative to the first connectingsurface.
 10. A prosthesis according to claim 8 in which each of thefirst connecting surface and the second connecting surface has an axis,and in which said axes are offset from each other in order to cause thefirst connecting surface to be offset from the second connectingsurface.
 11. A prosthesis according to claim 8 in which (a) the secondconnecting surface is inclined at an angle relative to the firstconnecting surface; and (b) the second connecting surface is offset fromthe first connecting surface.
 12. A modular humeral prosthesis accordingto claim 8 in which the first connecting surface is a female connectingsurface and the second connecting surface is a male connecting surface.13. A modular humeral prosthesis according to claim 8 in which theeccentric head comprises a trench at least partially surrounding theeccentric mating portion.
 14. A modular humeral prosthesis kit forreplacement of the humeral head of a humerus, comprising: (a) a stem tobe fitted to a resected humerus; (b) an eccentric head adapted toapproximate the size and shape of a humeral head, having an eccentricmating portion adapted to interface with an intermediate connectingmember; (c) a plurality of intermediate connecting members of which onemay be selected to connect the stem to the head, each intermediateconnecting member comprising: a first connecting surface forming acavity that is adapted to receive a structure that protrudes from thestem in order to mount the intermediate connecting member to the stem;and a second connecting surface adapted to be received in a cavity inthe head in order to mount the head to the intermediate connectingmember, the second connecting surface at least partially nested with thefirst connecting surface; the intermediate connecting members of the kitcomprising: at least one intermediate connecting member in which thefirst and second connecting surfaces share an axis of rotation; at leastone intermediate connecting member in which the first and secondconnecting surfaces are offset from each other; and at least oneintermediate connecting member in which the first and second connectingsurfaces are inclined at an angle relative to each other.
 15. Aprosthesis kit according to claim 14 in which both connecting surfacesare adapted to lock to corresponding structure using a tapered lockingmechanism.
 16. A prosthesis kit according to claim 14 in which theeccentric head comprises a trench at least partially surrounding theeccentric mating portion.
 17. A method of replacing a humeral head in apatient, comprising: (a) resecting the proximal end of the humerus toremove the head and expose the medullary canal of the humerus; (b)inserting a stem of a prosthesis into the medullary canal of theresected humerus, the prosthesis comprising: (i) the stem; (ii) aneccentric head adapted to approximate the size and shape of a humeralhead, having an eccentric mating portion adapted to interface with anintermediate connecting member; (iii) one of a plurality of intermediateconnecting members for connecting the stem to the head, eachintermediate connecting member including: a first, female, connectingsurface forming a cavity that is adapted to receive a structure thatprotrudes from the stem in order to mount the intermediate connectingmember to the stem; and a second, male, connecting surface adapted to bereceived in a cavity in the head in order to mount the head to theintermediate connecting member, the second connecting surface at leastpartially nested with the first connecting surface; the plurality ofintermediate connecting members including at least some members havingthe first and second surfaces being surfaces of rotation having axes ofrotation, the axis of rotation of the first surface non-collinear withthe axis of rotation of the second surface; (c) selecting a particularintermediate connecting member to provide a desired angle of inclinationof the head relative to the humerus; and (d) mounting and locking theintermediate connecting member to the stem, and mounting and locking theintermediate connecting member to the head, the mounting and locking ofthe intermediate connecting member to the stem and head imparting anydesired angle of inclination of the head relative to the humerus.
 18. Amethod according to claim 17 in which the eccentric head comprises atrench at least partially surrounding the eccentric mating portion. 19.A modular humeral prosthesis for replacement of the humeral head of ahumerus, comprising: (a) a stem adapted to be fitted to a resectedhumerus; (b) an eccentric head adapted to approximate the size and shapeof a humeral head, having an eccentric mating portion adapted tointerface with an intermediate connecting member; (c) an intermediateconnecting member for connecting the stem to the head, the intermediateconnecting member including: a first, female, connecting surface forminga cavity that is adapted to receive structure that protrudes from thestem in order to mount the intermediate connecting member to the stem;and a second, male, connecting surface adapted to be received in acavity in the head in order to mount the head to the intermediateconnecting member, the second connecting surface at least partiallynested with the first connecting surface and the first and secondsurfaces being non-coaxial.
 20. A modular humeral prosthesis accordingto claim 19 in which the eccentric head comprises a trench at leastpartially surrounding the eccentric mating portion.
 21. A modularhumeral prosthesis for replacement of the humeral head of a humerus,comprising: (a) a stem adapted to be fitted to a resected humerus; (b)an eccentric head adapted to approximate the size and shape of a humeralhead, having an eccentric mating portion adapted to interface with anintermediate connecting member; (c) an intermediate connecting memberfor connecting the stem to the head, the intermediate connecting memberincluding: a first, female, connecting surface forming a tapered,generally frustoconically shaped, cavity that is adapted to receive astructure that protrudes from the stem in order to mount and lock theintermediate connecting member to the stem; and a second, male,connecting surface that is generally frustoconically shaped, tapered,and adapted to be received in a cavity in the head in order to mount andlock the head to the intermediate connecting member, the secondconnecting surface at least partially nested with the first connectingsurface and the first and second surfaces being non-coaxial.
 22. Amodular humeral prosthesis according to claim 21 in which the eccentrichead comprises a trench at least partially surrounding the eccentricmating portion.
 23. A method of replacing a humeral head in a patient,comprising: (a) resecting the proximal end of the humerus to remove thehead and expose the medullary canal of the humerus; (b) inserting a stemof a prosthesis into the medullary canal of the resected humerus, theprosthesis comprising: (i) the stem; (ii) an eccentric head adapted toapproximate the size and shape of a humeral head, having an eccentricmating portion adapted to interface with an intermediate connectingmember; (iii) one of a plurality of intermediate connecting members forconnecting the stem to the head, each intermediate connecting memberincluding: a first connector formed as a surface of rotation and adaptedto cooperate with the stem in order to mount the intermediate connectingmember to the stem, a second connector formed as a surface of rotationand adapted to cooperate with the head in order to mount the head to theintermediate connecting member, the plurality of intermediate connectingmembers including at least some members having different angles ofinclination between their first and second connectors; (c) selecting aparticular intermediate connecting member to provide a desired angle ofinclination of the head relative to the humerus; and (d) mounting theintermediate connecting member to the stem, mounting the intermediateconnecting member to the head, the mounting of the intermediateconnecting member to the stem and head imparting the desired angle ofinclination of the head relative to the humerus.
 24. A method accordingto claim 23 in which the eccentric head comprises a trench at leastpartially surrounding the eccentric mating portion.
 25. A method ofreplacing a humeral head in a patient, comprising: (a) resecting theproximal end of the humerus to remove the head and expose the medullarycanal of the humerus; (b) inserting a stem of a prosthesis into themedullary canal of the resected humerus, the prosthesis comprising: (i)the stem; (ii) an eccentric head adapted to approximate the size andshape of a humeral head, having an eccentric mating portion adapted tointerface with an intermediate connecting member; (iii) one of aplurality of intermediate connecting members for connecting the stem tothe head, each intermediate connecting member including: a firstconnector formed as a surface of rotation and adapted to cooperate withthe stem in order to mount the intermediate connecting member to thestem, a second connector formed as a surface of rotation and adapted tocooperate with the head in order to mount the head to the intermediateconnecting member, the plurality of intermediate connecting membersincluding at least some members with each of the first connector andsecond connector having an axis, and in which said axes are offset fromeach other in order to cause the first connector to be offset from thesecond connector, (c) selecting a particular intermediate connectingmember to provide a desired offset of the head relative to the stem; and(d) mounting the intermediate connecting member to the stem, mountingthe intermediate connecting member to the head, the mounting of theintermediate connecting member to the stem and head imparting thedesired offset of the head relative to the humerus.
 26. A methodaccording to claim 25 in which the eccentric head comprises a trench atleast partially surrounding the eccentric mating portion.